Heat pump water heater with external inlet tube

ABSTRACT

A heat pump water heater system includes a water storage tank and a sealed heat pump cycle with a compressor, a condenser or gas cooler, an evaporator, and a refrigerant. The condenser/gas cooler is disposed in a heat exchange relationship with at least a portion of the water storage tank for heating water within the tank. The tank includes an outlet through which hot water is discharged, and a cold water inlet that is disposed so as to introduce cold water into the tank at a location of a bottommost portion of the condenser/gas cooler. The cold water introduced into the tank is not pre-heated by hot water in the tank so as to establish a thermodynamically efficient temperature differential between the cold water and hot water in the tank.

FIELD OF THE INVENTION

The present subject matter relates generally to water heaters, and moreparticularly to a heat pump water heater with an improved inlet tubedesign.

BACKGROUND OF THE INVENTION

Conventional electric resistance water heaters include a tank defining achamber for retention of water. A water inlet pipe connects to a coldwater supply line and relatively cold water into the chamber. Typically,the inlet pipe (“dip tube”) extends internally from the top of the tankto a location adjacent to the bottom of the tank. Within the tank,electric resistance elements (typically two) heat the water, which isdispensed from an outlet pipe located adjacent to the top of the tank.As hot water is dispensed, cold water is introduced into the bottom ofthe tank. As the water is heated, in rises in the tank.

Heat pump water heaters are gaining broader acceptance as a moreeconomic and ecologically-friendly alternative to electric waterheaters. These systems utilize a condenser configured in a heat exchangerelationship with the water storage tank, for example wrapped around thetank in a series of coils. During operation of the heat pump cycle, arefrigerant exits an evaporator as a superheated vapor and/or highquality vapor mixture. Upon exiting the evaporator, the refrigerantenters a compressor where the pressure and temperature increase and therefrigerant becomes a superheated vapor. The superheated vapor from thecompressor enters the condenser (or gas cooler in a transcriticalsystem), wherein the superheated vapor transfers energy to the waterwithin a storage tank and returns to a saturated liquid and/or highquality liquid vapor mixture.

Water heater tank designs developed for electric water heaters are,however, not particularly efficient for heat pump water heaters.Accordingly, it would be desirable to provide a water heater tank thatincreases the efficiency of the heat pump cycle in a heat pump waterheater.

BRIEF DESCRIPTION OF THE INVENTION

Aspects and advantages of the invention will be set forth in part in thefollowing description, or may be obvious from the description, or may belearned through practice of the invention.

In a particular embodiment, a heat pump water heater system is providedwith a water storage tank and a sealed heat pump cycle, which includes acompressor, a condenser/gas cooler, an evaporator, and a refrigerant.The condenser/gas cooler is disposed in a heat exchange relationshipwith at least a portion of the water storage tank for heating waterwithin the tank. The tank further includes an outlet through which hotwater is discharged, and a cold water inlet that is disposed tointroduce cold water into the tank at a location of a bottommost portionof the condenser. With this configuration, cold water introduced intothe tank is not pre-heated by hot water in the tank so as to enhance thethermodynamic cycle efficiency of the system by increasing thetemperature range over which heat is rejected from the condenser/gascooler.

The system may include an inlet pipe that is disposed externally of thetank and connected to the cold water inlet, which is disposed proximateto a bottom of the tank.

In a particular embodiment, the condenser/gas cooler is a coiled heatexchanger wrapped around the tank and having a refrigerant inletdisposed proximate to the cold water inlet and a refrigerant outletdisposed proximate to a top of the tank.

In still another embodiment, the system may include a generallyhorizontally disposed cold water discharge pipe within the tankconnected to the cold water inlet and having outlets disposed along thelength of the pipe. The outlets may be oriented towards a bottom of thetank.

The system may include a supplemental heat source, such as one or moresupplemental electric resistive heating element within the tank.

The present invention also encompasses a water storage tank apparatusthat is particularly suited for use in a heat pump water heater system.The tank apparatus includes a tank in which cold water introduced intothe tank is heated and discharged as hot water. A refrigerantcondenser/gas cooler is configured in a heat exchange relationship withat least a portion of the tank. The tank further includes an outletthrough which hot water is discharged, and a cold water inlet that isdisposed so as to introduce cold water into the tank at the location ofa bottommost portion of the condenser/gas cooler.

The tank apparatus may include an inlet pipe that is disposed externallyof the tank and connected to the cold water inlet, which is disposedproximate to a bottom of the tank.

In a particular embodiment, the condenser/gas cooler is a coiled heatexchanger wrapped around the tank and having a refrigerant inletdisposed proximate to the cold water inlet and a refrigerant outletdisposed proximate to a top of the tank.

In still another embodiment, the tank apparatus may include a generallyhorizontally disposed cold water discharge pipe within the tankconnected to the cold water inlet and having outlets disposed along thelength of the pipe. The outlets may be oriented towards a bottom of thetank.

The tank apparatus may include a supplement heat source, such as one ormore supplemental electric resistive heating elements within the tank.

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdescription and appended claims. The accompanying drawings, which areincorporated in and constitute a part of this specification, illustrateembodiments of the invention and, together with the description, serveto explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth in the specification, which makes reference to the appendedfigures, in which:

FIG. 1 is a diagram view of a conventional heat pump water heatersystem;

FIG. 2 is a view of an embodiment of a heat pump water storage tank inaccordance with aspects of the invention;

FIG. 3 is a view of an alternative embodiment of a heat pump waterstorage tank in accordance with aspects of the invention; and

FIG. 4 is a diagram view of a heat pump water heater systemincorporating still a further embodiment of a water storage tank inaccordance with aspects of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference now will be made in detail to embodiments of the invention,one or more examples of which are illustrated in the drawings. Eachexample is provided by way of explanation of the invention, notlimitation of the invention. In fact, it will be apparent to thoseskilled in the art that various modifications and variations can be madein the present invention without departing from the scope or spirit ofthe invention. For instance, features illustrated or described as partof one embodiment can be used with another embodiment to yield a stillfurther embodiment. Thus, it is intended that the present inventioncovers such modifications and variations as come within the scope of theappended claims and their equivalents.

Referring now to the figures, FIG. 1 depicts a heat pump water heater(HPWH) system 100 that includes an evaporator 102, a compressor 130, acondenser 108, a throttling device 106, and at least one fan 104. Thecondenser 108 is assembled in a heat exchange relationship with thewater storage tank 120 to heat the water within the tank. Duringoperation of the heat pump cycle, a refrigerant exits the evaporator 102as a fluid in the form of a superheated vapor and/or high quality vapormixture. Upon exiting the evaporator 102, the refrigerant enters thecompressor 130 wherein the pressure and temperature of the refrigerantare increased such that the refrigerant becomes a superheated vapor. Thesuperheated vapor from the compressor 130 enters the condenser 108wherein it transfers energy to the water within a storage tank 120 andcondenses into a saturated liquid and/or high quality liquid vapormixture. This high quality/saturated liquid vapor mixture exits thecondenser 108 and travels through the throttling device 106. Uponexiting the throttling device 106, the pressure and temperature of therefrigerant drop at which time the refrigerant enters evaporator 102 andthe cycle repeats itself.

In an alternate embodiment, the HPWH system 100 is a transcriticalsystem wherein the refrigerant (typically CO2) has a low critical pointand thus operates on a transcritical cycle wherein it evaporates in thesubcritical region and rejects (transfers) heat at temperatures abovethe critical point in a “gas cooler” instead of a condenser. It shouldthus be appreciated that element 108 discussed herein may also be a gascooler depending on the type of system.

The water storage tank 120 in the system 100 of FIG. 1 is a conventionaldesign wherein a water inlet line 112 is provided for directing coldwater to the bottom of the tank 120 via a dip tube 110 such that thewater is preheated by the water in the tank before it discharges intothe tank at the outlet of the dip tube 110.

The system 100 may also include supplemental electric heating elements122 and 124 placed near the top and bottom of the water storage tank 120to heat the water.

The heated water exits the tank 120 at exit 114 and flows to theresidence or other place where heated water is desired. The system 100may include a temperature sensor 126 positioned to sense the temperatureof the water in the upper region of the tank and may also haveadditional temperature sensors placed at various locations for sensingother temperatures, such as heat pump condenser inlet and outlettemperatures, ambient temperature, etc.

The system 100 may also include a controller 152, equipped with amicroprocessor, that determines which of the compressor 130, an upperelectric resistance heater 122, and a lower electric resistance heater124 shall be energized, and for how long, in order to heat the waterwithin the water storage tank 120. The controller 152 may receive anymanner of temperature readings (e.g., from sensor 126), flow signals,setpoints, and so forth, to implement its control functions.

FIGS. 2 and 3 depict embodiments of a water storage tank apparatus 220in accordance with aspects of the invention, and FIG. 4 depicts yetanother embodiment of a tank apparatus 220 installed within a heat pumpwater heater system 200. With respect to FIG. 4, it should beappreciated that the invention encompasses any manner of heat pump waterheater system 200 that incorporates a water storage tank in accordancewith aspects of the invention, and that the configuration of the system200 depicted in FIG. 4 is for illustrative purposes only.

FIG. 2 depicts an embodiment of a water storage tank apparatus 220 thatmay be configured into any suitable heat pump water heater system 200(FIG. 4). In the embodiment of FIG. 2, the storage tank apparatus 220includes a tank 222 that may be surrounded by a shell component 224. Anymanner of suitable thermal insulating material may be disposed withinthe space between the shell 224 and tank 222, as is well known in theart. The tank 222 includes a bottom 223 having a cold water inlet 232disposed proximate thereto. The tank 222 receives cold water via thecold water inlet 232, heats the water, and discharges the water througha hot water outlet 230 proximate to a top portion of the tank 222.

A heat pump refrigerant condenser/gas cooler 226 is configured in a heatexchange relationship around at least a portion of the tank 222,depending on the particular configuration of the condenser/gas cooler226. For example, the condenser/gas cooler 226 may be a planar orplate-like heat exchanger that is wrapped at least partially around thetank 222. In the illustrated embodiment, the condenser/gas cooler 226 isa coiled loop heat exchanger 228 having a plurality of tube coilswrapped around at least a portion of the tank 222. These coils may bedisposed between the shell 224 and the tank 222, as depicted in FIG. 2.

In the embodiment of FIG. 2, refrigerant from a compressor 212 (FIG. 4)is introduced at a refrigerant inlet 240 to the condenser/gas cooler 226at a location proximate to a top portion of the tank 222. Therefrigerant circulates through the coils of the heat exchanger 228 andexits at a refrigerant outlet 242. Thus, in this particularconfiguration, the “hot” refrigerant is introduced at the top portion ofthe tank 222 and the “cold” refrigerant exits at a location proximate tothe bottom 223 of the tank generally at a location corresponding to thecold water inlet 232.

In the embodiment of FIG. 3, the directional flow of the refrigerantthrough the coiled heat exchanger 228 is opposite of that depicted inFIG. 2. In other words, the “hot” refrigerant enters the coiled heatexchanger 228 at the refrigerant inlet 240 proximate to the bottom 223of the tank generally at the location of the cold water inlet 232, andthe “cold” refrigerant exits at the refrigerant outlet 242 generallyproximate to the top portion of the tank. The configuration of FIG. 3may be desired in that an even greater temperature gradient is definedin the tank, which may further enhance thermodynamic efficiency byallowing heat rejection from the condenser/gas cooler 226 across a widertemperature range, as compared to the embodiment of FIG. 2 wherein theinitial “hot” refrigerant is exposed in an initial heat-exchangerelationship with the relatively hotter water within the tank at the topportion of the tank 222.

Referring still to FIGS. 2 and 3, the cold water inlet 232 may besupplied with cold water via an inlet pipe 234 that is disposedalongside of the tank 222. It should be appreciated, however, that anymanner of suitable piping arrangement may be utilized to conduct coldwater into the tank at a location of the colder water inlet 232generally proximate to the bottom portion of the tank 223.

The operative location of the cold water inlet 232 and the condenser/gascooler 226 may vary relative to each other. In general, however, it isdesired that the cold water be introduced into the tank at a locationthat generally corresponds to the lower portion of the coiled heatexchanger 228 (regardless of the directional flow of the refrigerant).It is not beneficial for a cold “slug” of water to settle at the bottomportion of the tank 222 without being sufficiently heated by thecondenser 226. This situation would result in a relatively stagnatethermal layer of cold water at the bottom portion of the tank withoutnecessarily improving the thermodynamic efficiency of the heat pumpsystem.

Referring to FIG. 4, the embodiment of the water storage tank apparatus220 includes a discharge pipe 236 connected to the cold water inlet 232.This discharge pipe includes any configuration of outlets 232 that serveto uniformly distribute the cold water introduced into the tank 222across the diameter of the tank. The outlets 238 may be disposed so asto direct the cold water towards the bottom 223 of the tank so as toenhance thermal stratification within the tank.

The storage tank apparatus 220 in FIG. 4 also includes a supplementalheating source, such as one or more electric resistive heating elements244, with one element 244 disposed proximate to the top portion of thetank and the other element 244 disposed proximate to a bottom portion ofthe tank 222. The use of supplement electric resistive heating elementsin a heat pump hot water system is known in the art and need not bedescribed in detail herein. In general, the heating elements 244 areactivated by a controller 210 in situations wherein the demand of hotwater placed on the system 200 exceeds the heating capability of theheat pump thermal cycle.

FIG. 4 further depicts the water storage tank apparatus 220 placed in aheat pump cycle utilizing a compressor 212, and evaporator 202, a fan204, and a throttle device 206. The operation of these components isdescribed above with respect to FIG. 1 and need not be repeated herein.The controller 210 may be configured with the compressor 212 and theresistive heating elements 244 and be responsive to any manner of inputsignals, such as temperature of water within the tank, flow of water outof the tank, thermostat set points, and the like, to coordinateoperation of the system.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they include structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

What is claimed is:
 1. A heat pump water heater system, comprising: awater storage tank; a sealed heat pump cycle, comprising a compressor, acondenser/gas cooler, an evaporator, and a refrigerant, wherein saidcondenser is disposed in a heat exchange relationship with at least aportion of said water storage tank for heating water within said tank;and said tank further comprising an outlet through which hot water isdischarged, and a cold water inlet that is disposed so as to introducecold water into said tank at a location of a bottommost portion of saidcondenser/gas cooler; wherein cold water introduced into said tank isnot pre-heated by hot water in said tank so as to establish athermodynamically efficient temperature differential between the coldwater and hot water within said tank.
 2. The heat pump water system asin claim 1, further comprising an inlet pipe that is disposed externallyof said tank, said cold water inlet disposed proximate to a bottom ofsaid tank, and said inlet pipe connected to said cold water inlet. 3.The heat pump water system as in claim 1, wherein said condenser/gascooler comprises a coiled heat exchanger wrapped around said tank, saidheat exchanger comprising a refrigerant inlet disposed proximate to saidcold water inlet and a refrigerant outlet disposed proximate to a top ofsaid tank.
 4. The heat pump water system as in claim 1, furthercomprising a generally horizontally disposed cold water discharge pipewithin said tank connected to said cold water inlet, said discharge pipecomprising outlets disposed along the length thereof.
 5. The heat pumpwater system as in claim 4, wherein said outlets are oriented towards abottom of said tank.
 6. The heat pump water system as in claim 1,further comprising at least one supplemental electric resistive heatingelement within said tank.
 7. A water storage tank apparatus for a heatpump water heater system, comprising: a tank in which cold waterintroduced into said tank is heated and discharged as hot water; arefrigerant condenser/gas cooler configured in a heat exchangerelationship with at least a portion of said tank; and said tank furthercomprising an outlet through which hot water is discharged, and a coldwater inlet that is disposed so as to introduce cold water into saidtank at a location of a bottommost portion of said condenser/gas cooler;wherein cold water introduced into said tank is not pre-heated by hotwater in said tank so as to establish a thermodynamically efficienttemperature differential between the cold water and hot water withinsaid tank.
 8. The water storage tank apparatus as in claim 7, furthercomprising an inlet pipe that is disposed externally of said tank, saidcold water inlet disposed proximate to a bottom of said tank, and saidinlet pipe connected to said cold water inlet.
 9. The water storage tankapparatus as in claim 7, wherein said condenser/gas cooler comprises acoiled heat exchanger wrapped around said tank, said heat exchangercomprising a refrigerant inlet disposed proximate to said cold waterinlet and a refrigerant outlet disposed proximate to a top of said tank.10. The water storage tank apparatus as in claim 7, further comprising agenerally horizontally disposed cold water discharge pipe within saidtank connected to said cold water inlet, said discharge pipe comprisingoutlets disposed along the length thereof.
 11. The water storage tankapparatus as in claim 10, wherein said outlets are oriented towards abottom of said tank.
 12. The water storage tank apparatus as in claim 7,further comprising at least one supplemental electric resistive heatingelement within said tank.